Abstract: The invention relates to a manufacturing method for making an unwrought semi-finished product having at mid thickness a density of micropores of size greater than 90 ?m less than 50% and preferably less than 20% of the density of micropores of size greater than 90 ?m obtained by a method according to prior art. The method according to the invention comprises in particular an ultrasound treatment step for the molten metal bath in a furnace and/or a vessel using an immersed device comprising at least one ultrasound transmitter. The semi-finished products obtained according to the method of the invention are particularly advantageous for manufacturing by rolling sheets designed for the aircraft industry to produce spars, ribs, upper and lower wing skins and for manufacturing by extrusion sections designed for the aircraft industry to produce stiffeners.